The present application claims priority under 35 U.S.C. xc2xa7 119 of German Patent Application No. 100 00 181.5, filed on Jan. 5, 2000, the disclosure of which is expressly incorporated by reference herein in its entirety.
1. Field of the Invention
The present invention is directed to a process for dissolving used paper.
2. Discussion of Background Information
It is known that processes of the above-mentioned type are performed in such a way that the used paper is supplied to a pulper in the state in which it was delivered to the paper factory. Here, this pulper serves to mix in water and to dissolve the paper webs. If necessary, a station for removing bale wires or bale edges can be provided before the pulper. As a rule, all components of the used paper bale, possibly without these wires or edges, are dropped into the pulper and are mechanically processed with more or less intensity. Besides the high energy consumption in the pulper, another undesired result of the known process can be a breaking down of non-fibrous attendant materials to the extent that it becomes difficult to remove these particles. The large amount of such foreign materials arriving in the suspension necessitates a high sorting and cleaning expenditure.
DE 34 39 098 A1 discloses, e.g., a process in which, before the dissolution in the pulper, several grinding and cleaning steps are performed on the used paper, which is not yet in a suspension. While this process is good and effective, it is also expensive.
A system is known, e.g., from DE 197 53 202 A1, that is used to process packaging waste. The purpose of this process is to attain plastics that are sorted by type. In this process, a type of used paper occurs as well, which exists as air-dry pieces or scraps of paper and already has a certain degree of purity; however, it is not free of impurities, in particular adhering plastic films, for example, of beverage cartons.
The present invention provides a process with which it is possible to process the waste paper into a paper fiber suspension continually and in as economical a manner as possible, preferably in such a way that the conventional used paper pulper and an expensive coarse sorting can be eliminated.
According to the invention, the process for dissolving used paper includes adjustment of the content of solid particles of the used paper, e.g., by the introduction of water, to a range between about 15 and 35%, kneading with a specific work of at least about 10 kWh/t, subsequent dilution to a content of solid particles below about 6%, subsequent separation of non-fibrous contaminants, e.g., plastic films, with the aid of a wet screening, subsequent adjustment to a solid material content of less than about 3%, and preferably less than about 2%, and subsequent separation of heavy particles with the aid of hydrocyclones.
Therefore, in this process of the instant invention, delivered used paper is used as a raw material which, at the beginning of processing, is in pieces (paper scraps) due to breaking up of the paper webs, and, instead of being sent to a pulper, is sent directly to a used paper kneading device. At the water content provided, this device is in a position to perform a function that would otherwise be possible in a pulper. It is favorable for such kneading devices to be able to be operated continuously. However, pulpers that can be used for such raw materials are ideally operated in batches. This is especially true for high-consistency pulpers in the consistency range of about 8 to 15%.
The dissolving effect can be increased by heating the used paper. However, this temperature must be adjusted to impurities still present in the used paper in order to prevent undesired grinding of soft, non-fibrous impurities. In such raw materials, plastic coatings are often present on the paper webs that are relatively thin and easily torn, even if not as easily as paper webs that have been swollen by water. It is precisely these impurities that can be removed in a particularly effective and economical fashion in the subsequent mid-consistency sorting. In special cases, a thin stock sorting can occur instead of the mid-consistency sorting, which leads to greater success, but also to a higher expenditure. The impurities that are very small and have not yet been removed, in particular, small, heavy particles, can be removed in the subsequent hydrocyclone treatment, for which purpose highly effective cleaners are particularly well-suited.
Accordingly, the instant invention is directed to a process for dissolving used paper including adjusting a content of solid particles of used paper to a range between about 15 and 35%, kneading the used paper with a specific work of at least about 10 kWh/t, diluting the kneaded used paper to a content of solid particles below about 6%, separating non-fibrous contaminants with wet screening, adjusting a solid material content to less than about 3%, and separating heavy particles with at least one hydrocyclone.
In accordance with a feature of the invention, the content of solid particles of used paper can be adjusted by introducing water, non-fibrous contaminants may include plastic films, and the solid material content can be adjusted to less than about 2%.
According to another feature of the instant invention, the wet screening may be performed at a consistency of between about 2 and 5%.
Further, the wet screening may be performed in a wet screener with round screen openings having a diameter of about 1-3 mm. The wet screener may remove at least about 80% of the non-fibrous contaminants contained in the used paper during kneading. The non-fibrous contaminants may include plastic film.
According to still another feature of the present invention, the wet screening may be performed in at least one pressure sorter.
In accordance with a further feature, a temperature of the used paper during kneading can exceed 80xc2x0 C.
According to a still further feature of the present invention, the content of solid particles of used paper before kneading can be adjusted by being sprayed with water.
Moreover, the kneading can occur in a single-wall shredder. The single-wall shredder may include kneading tools moved relative to one another at a speed of no greater than about 15 m/sec and at a distance from one another of at least about 10 mm.
Further still, the kneading may occur in a double-wall shredder. The kneading may be performed for at least about 2 minutes.
According to another feature of the instant invention, the kneading may be performed in a disk disperser having rows of teeth that engage one another.
Further, the kneading may be performed in a rotating drum including at least one moving grinding element. A radial extension of the grinding element can be at least about 10% of a diameter of the rotating drum.
The kneading may be performed in a rotating drum including a fixed displacer that forms a kneading zone between the fixed displacer and the rotating drum.
In accordance with still another feature of the invention, the kneading may be performed continuously. The process can also include adjusting and regulating an intensity of the kneading according to at least one quality value of the used paper determined after kneading. The at least one quality value may include whiteness achieved in a subsequent deinking.
The process may also include breaking up the used paper that is not suspended up before kneading to such an extent that a majority of the webs or sheets have been torn up several times. The process can also include removing coarse impurities from the used paper before kneading. The coarse impurities may include coarse heavy portions. Further, the process can include removing iron pieces before kneading with a magnetic separator. The process may also include removing bale binding wires before kneading.
According to still another feature of the instant invention, the process may include removing heavy particles from the suspension with cleaners whose field of force is more than 500 times the acceleration due to gravity.
The process can also include removing, in a deinking arrangement, fine impurities from the kneaded and suspended used paper. The fine impurities can include printing inks. The deinking arrangement may be connected downstream of the hydrocyclones.
In accordance with another feature of the invention, no pulper is used in the process, and no dissolving drum with a pure falling effect is used.
Moreover, no sorting is performed at consistencies less than about 2%, and no hydrocyclones are used at consistencies greater than about 2%.
According to a further feature of the present invention, the process may be performed continuously.
In accordance with a still further feature of the invention, the amount of water added can be adjusted in accordance with an amount of used paper to be dissolved.
In accordance with a further feature of the present invention, the amount of water added may be adjusted in accordance with a power consumption for kneading, thereby regulating the power consumption.
According to yet another feature of the present invention, the amount of water added can be adjusted to a power consumption for kneading and to an amount of used paper, thereby regulating the specific work of the kneading.
The present invention is directed to a process for dissolving used paper that includes kneading used paper having a solid particle content of between about 15 and 35% with a specific work of at least about 10 kWh/t, diluting the kneaded used paper to a content of solid particles below about 6%, separating non-fibrous contaminants in the diluted kneaded used paper with wet screening, adjusting a solid material content of the wet screened used paper to less than about 3%, and separating heavy particles from the wet screened used paper after the solid material content has been adjusted with at least one hydrocyclone.
Other exemplary embodiments and advantages of the present invention may be ascertained by reviewing the present disclosure and the accompanying drawing.